Keeping Up with Growth:Lakeville Water Plant Expands with Population

Lakeville,
Minnesota, is typical of the outer ring of suburbs in the Minneapolis-St.
Paul metropolitan area. As the overall population gets larger, and as
people have a desire to live farther out, the suburbs are experiencing
a boom in residents that challenges the services that must be delivered
to them.

In the past 10 years, Lakeville has not only built its first water treatment
plant, it has expanded it once, and it now looks ahead to a further expansion. The
plant was population driven, says Don Volk, the citys director
of public works. People moving to Lakeville from Minneapolis and
St. Paul were used to good quality water, including water that had been
softened.

Lakeville does biennial surveys of its citizens. In the early 1990s,
there were consistent complaints about discoloration of fixtures caused
by iron in the water. At the time, Lakeville had no treatment plant.
Fluoride and chlorine were added at each well site along with a polyphosphate
to sequester iron and manganese. However, iron was still turning up in
the finished water.

In 1992, the city council authorized a comprehensive water plan update.
Two years later, the design-process approval for a water treatment facility
began. This coincided with Volk coming to Lakeville from the city of
Lino Lakes. They ran a pilot plant for three months to test oxidants,
media types, and length of filter runs, said Naeem Qureshi of Progressive
Consulting Engineers of Minneapolis. They got good filter runs
with both anthracite/greensand and anthrafill. They decided to go with
greensand/anthracite.

The plan called for a greensand-filtration plant for iron and manganese
removal with an initial capacity of 10 million gallons per day (MGD)
and the ability to expand, in two separate stages, to 30 MGD. Construction
began in 1996, and the original plant went on-line in 1998.

Don Volk has been with the city of Lakeville
since 1994.

A barn on the site has been converted into
a storage shed.

Sources
Ten wells now provide water to the plant. Six of the wells were already
in use before the original plant was built. One well was added shortly
after the plant was opened, and two additional wells were added at
the time the plant was expanded to 20 MGD in 2001. The newest well
was brought on-line in 2003.

Four more wells, which were present before the plant, are now just used
for peak demand. Fluoride and chorine are added at the well sites with
the water directly entering the distribution system. Volk says that the
well field will eventually be expanded to encompass two of these wells
and have them feed the plant.

All of the water is from the Prairie du Chien-Jordan aquifer, which
is high in iron and manganese. Some of the wells also have radium, although
the levels are reduced to acceptable amounts through blending with water
from other wells.

Treatment
Pretreatment consists of heavy doses of chlorine to help the iron oxidize
before it gets to the filters. Using chlorine rather than air as an oxidant
lowers the operation and maintenance costs, according to Volk.

The original plant had four filters. The 2001 expansion to increase
the capacity to 20 MGD added four more filters. The water goes from the
filters to a clearwell. Water from the clearwell is used to backwash
the filters. The backwash water is then routed through a plate settler
to remove the highly concentrated iron and manganese. After it settles,
the iron and manganese slurry goes to the sanitary sewer with the rest
of the water going to a washwater treatment building and then back to
the front of the plant. Volk says they reuse about 80 percent of their
backwash water.

Before the water is pumped to the system, additional chlorine is added
as necessary to maintain a residual. The amount added depends on much
was used up in oxidizing the iron and manganese in the pre-treatment
state.

A schematic of the Lakeville Water Treatment Plant.

Controls
The original plant included two manual instrument panels as redundancy
for the System Control and Data Acquisition (SCADA) system. In
1996, we werent as confident in the reliability of computers
so we wanted a backup to not totally rely on computers, Volk
explained. Each manual instrument panel controls two of the filters
from the original plant. With more faith in computers, the utility
did not install manual controls with the new filters as part of the
2001 expansion.

Performance
Within three months of the opening of the original plant in 1998, complaints
about the water dropped to almost none. Volk says that, with the treatment,
levels of iron in the finished water are well below .3 parts per million
(ppm) and below .05 ppm for manganese. Volk added that they continued
their normal biennial water-main flushing for a few years but as a
result of the low iron and manganese levels have now discontinued that.

Meeting Future Growth
The plant is designed to be expanded to 30 MGD, and the final expansion
may take place in the latter part of this decade. Volk hopes that this
expansion, along with water conservation, will take them to full population
growth, which is expected to be 97,000 (the citys population
is now approximately 46,000). Otherwise, Volk says, we
may need another plant.

Regarding conservation, in 2004 the city will go to an odd-even sprinkling
schedule for its residents. Even though such a program has been voluntary
in the past, Volk says compliance has been outstanding.

Another issue that affects conservation is the low water rates, which
are based only on operation, not infrastructure, costs. Volk says they
are considering a tiered rate structure to discourage excess water usage,
although educating the public has been effective to this point. Lakeville
residents respond very well, he adds.

Added Features
The original project included construction of a maintenance facility
for the utility department and renovation of a barn on the sitewhich
had been a farmsteadto use for storage for the citys police
and public works departments. The maintenance facility includes a community
meeting room that is used by businesses and community organizations.
The room, Volk says, helps draw attention to what were
proud of-our water treatment facility.

Volk has hosted a number of tours of the plant, especially for students.
Picture boards around the plant are popular and help illustrate the workings
of a public water system. Upgrades in security in the past two-and-a-half
years havent eliminated the school groups from visiting. If the
Homeland Security Threat Level rises from yellow (elevated) to orange
(high), they suspend tours. Otherwise, they welcome visitors as usual
although they do background checks on the adults.

Costs
The original 10 MGD plant cost $15 million. The 10 MGD expansion in late
2001 was $5.5 million.